Rainwater-limestone-basalt reactions

[Dawn Dela Vega]

Hi everyone! I am an undergraduate student who was recently introduced to the GWB software packages (mainly the Rxn module). I would appreciate some guidance on approaching this practice problem: how can I model the potential reactions when atmospheric CO2 reacts with rainwater over a limestone outcrop underlain by basalts?

Do you know how I can model this situation? Apart from knowing I'll need the React module, I am very much lost entirely. 

Thank you so much!

[Jia Wang]

Hello,

It is rather difficult to give advice on what might be the most suitable. There are a couple of ways to incorporate gases into your system. If the CO2 is in equilibrium with the initial fluid, you can swap it for a component in the initial system and set the partial pressure or fugacity value. This will tell this program to calculate the corresponding dissolved concentration in fluid. If you are creating a CO2 rich fluid, you can simulate that with a titration path and then use the pickup feature to set that fluid as your starting point. Mineral reactions can be treated with the equilibrium approach or kinetically.

If you had only worked with the Rxn application before, I recommend checking out the GWB Essentials Guide, starting in Section 2 Configuring the Programs. This will help you understand how to set up and calculate chemical speciation of the initial system chemistry, which is shared across many of the GWB applications. Once you are comfortable with configuring the initial system and working with static systems, you can advance to working with React and simulating dynamic systems (see section 2 using React in the GWB Reaction Modeling Guide). React allows you to add in reactants which allows to alter the initial system based on various types of the reaction pathways. You can review all types of reaction pathways in the GWB Reaction Modeling Guide and see which type best suits your needs. A plethora of example scripts are installed in the Script folder, where your GWB software is installed.

Hope this helps,
Jia Wang
Aqueous Solutions LLC